Electro-magnetic clamp for gripping a shaft

ABSTRACT

A clamp for locking engagement with a shaft includes a body having a bore for slideably receiving a shaft, with opposing grippers recessed into the body coaxial with the shaft. The grippers each include inner and outer sleeves displaceable relative to each other, with the outer sleeves being retained by shoulders within the body and the inner sleeves being slideable within a pocket for selectively releasing and gripping the shaft. A pair of opposing plungers selectively displaces the inner sleeves, the plungers each being associated with a slideable arm for coordinated gripping and release of the shaft. The arms are drawn together or apart by an actuator such as a solenoid. The clamp is intended to be fastened to a component, for permitting the component to selectively grip a shaft, or release the shaft for slideable and/or rotateable movement relative to the shaft, such as an optical instrument for testing of patient&#39;s eyes which when fastened must tightly grip a shaft to prevent rotation and slideable movement, but which when released must permit free movement relative to the shaft.

FIELD OF THE INVENTION

The invention relates to a releasable clamp for gripping a shaft, forholding a component in a selected fixed position relative to a shaft.

BACKGROUND OF THE INVENTION

Mechanical and electro-mechanical devices for holding a component inposition in relation to a shaft have applications in many fields. Forexample, an optical device for measuring a patient's eyes must beprecisely positioned in relation to the patient, requiring that thedevice be freely moveable along a shaft until it reaches the correctposition, at which time it must be clamped to the shaft in a releasablefashion but which holds it firmly in place. Numerous other applicationsexist for a clamp which releasably holds a component in a fixed positionalong a shaft, but which may be readily released to permit eithersliding or rotary movement or both. Existing clamps may comprise a clampbody which supports a pair of angled plates having an aperturetherethrough, the plates being pivotable about one end such that a shaftpassing through the plates may slide or rotate freely therethrough whenthe plates are steeply angled relative to the shaft, but is preventedfrom moving when the plates are more shallowly angled. However, thistype of system is subject to a high level of wear and other drawbacks.Other systems have been proposed, all of which involve a relatively highdegree of complexity. There is a need for a relatively simple, effectiveclamp suitable for actuation by electromagnetic means such as a solenoidmotor.

A variety of mechanical clamping systems have been proposed forreleasably fixing a component to a shaft in a manner such that thecomponent may be readily re-positioned on the shaft. For example, U.S.Pat. No. 5,052,842 to Janatka discloses a slotted hub having a centralbore for receiving a shaft, with a screw to tighten the collar aroundthe shaft for locking engagement. In a somewhat similar fashion, U.S.Pat. No. 4,142,811 to Burnham discloses a hub having a central bore,with the hub being perforated with threaded openings to receive aplurality of screws which when tightened directly or indirectly contacta shaft extending through the bore. Upon tightening the screws, contactis made with the shaft thereby locking the shaft relative to the hub.

Another type of locking system is disclosed in U.S. Pat. No. 4,893,810,the commercial embodiment of which is the “Grip Fast™” collar, and isspecifically intended for locking athletic weights to a barbell shaft.The collar comprises concentric inner and outer sleeves, the innersleeve having a plurality of openings to receive bearings extendingpartway through the openings. A plurality of wedges are positioned tocontact the bearings, such that when the outer sleeve is alignedrelative to the inner sleeve, the bearings are wedged inwardly andextend through the inner sleeve so as to contact and lock the shaft inposition. Axial displacement of the sleeves relative to each otherpermits the bearings to retract, thereby releasing the shaft. The innerand outer shafts are spring biased relative to each other so as tomaintain the locked position until the user retracts the outer sleeve.Similar locking systems are disclosed in U.S. Pat. Nos. 4,395,051 and4,453,449.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved clamp forreleasably fastening a component along a shaft, such that when releasedthe component may be rotated or slid along the shaft, or both rotatedand slideably displaced, and which when engaged, prevents either axialor rotary movement, or both, relative to the shaft. A further embodimentis to provide such a clamp which may be actuated by an electromagneticcomponent such as a solenoid.

In one aspect, the invention relates to a clamp for gripping an elongateshaft comprising a clamp body having a bore for slideably receiving theshaft. Within the body is provided at least two opposing shaft gripperscoaxial with the bore for selectively gripping the shaft. The shaftgrippers are of the type comprising a pair of concentric sleevesdisplaceable relative to each other, whereby when aligned the outersleeve urges bearings or other contact members to press against theshaft so as to firmly grip the shaft to prevent movement relative to thegripper, and when displaced the contact members retract to release theshaft. Alternatively, the gripping may occur when the sleeves aredisplaced relative to each other and release when aligned. Typically,such grippers are most effective only in a single direction, since aretraction of the shaft in a first direction cooperates with the wedgingaction of the contact members, while retraction in an opposed directionwill release the gripper. Thus, in order to prevent shaft slippage ineither axial direction, it is desirable to provide a pair of gripperswithin the clamp body, aligned along the shaft and in opposingdirections whereby they may be simultaneously actuated for gripping orreleasing the shaft.

In order to actuate the grippers, a pair of opposing plungers isprovided for contacting the inner sleeve of each gripper so as to urgethe inner sleeve inwardly towards the centre of the body, so as torelease the shaft. The grippers are recessed into the clamp body. Theouter sleeve of each gripper is fixed in position, by abutting against ashoulder within the interior of the clamp body. The inner sleeve canmove axially within a pocket inboard of the shoulder. The plungers areeach operatively connected to an arm extending outwardly from the body,the arm mounted to the body for sliding movement in a direction axial tothe shaft. For example, the arm may be engaged to the body by means ofone or more guide pins. Conveniently, the arms include an opening topermit the shaft to pass through the arm, such that the arms may bepositioned on either end of the body in a generally central position.Drawing the arms towards each other will thus urge the plungers inwardlytowards each other, thereby releasing the shaft so as to slide androtate freely within the clamp body, while urging the arms apart fromeach other has the opposite effect. It will be readily seen that theinvention may work equally well in the reverse direction, whereby thegrippers operate in the reverse direction and urging the arms apartwould serve to grip the shaft to the clamp body.

The grippers may be biased so as to urge the arms apart so as to fixedlyengage the shaft unless the arms are urged together by a user to releasethe shaft. A solenoid motor or other linear actuator may join therespective arms, the motor being actuated by a controller so as torapidly release or engage the grippers by urging the arms together orapart.

The body is conveniently provided with bosses or other fasteners topermit the attachment of components. The bosses may permit therotateable attachment of components to the clamp body.

The present invention will now be further described by way of a detaileddescription of a preferred embodiment. It will be understood that thisdescription merely illustrates an example of the invention and is notintended to limit the scope of the invention in any respect. Rather, afull scope of the invention is described in this specification as awhole, including the claims. It will be understood that unless otherwisespecified, any element or component described herein may be replaced byan obvious mechanical equivalent. Further, directional or geometricreferences herein are not intended to be read in a strictly limitingsense, for example a reference to a “cylindrical shaft” may include ashaft having a non-circular cross-section. In similar fashion,directional references herein are generally provided merely forconvenience of description. It will be understood that the invention maybe readily used in any orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the clamp, partly in section toillustrate the internal components.

FIG. 2 is a side elevational view of the clamp body, showing internalelements in dotted lines.

FIG. 3 is a front elevational view of the clamp.

FIG. 4 is a perspective view of the clamp body.

FIG. 5 is a perspective view of the clamp body engaged to a shaft andmounted to an optical component.

FIG. 6 is a sectional view of an example of a prior art gripper for usein the present invention.

DETAILED DESCRIPTION

Referring to the Figures, the clamp body 10 comprises a suitable rigidmaterial, such as a metal such as stainless steel or aluminum, orinjection-molded plastic. The body includes a central bore 12 forreceiving the shaft 14 in a manner which permits the shaft to slide androtate freely within the bore when the clamp is in the releasedposition. The bore is symmetrical about its elongate axis, with widenedcylindrical recesses 16 at each of its opposed, outboard ends to receivea pair of opposed grippers 24, described below. The recesses 16 open tothe opposed ends 18 of the body. The base of each recess 16 is inwardlystepped and comprises an annular shoulder 20 for abutting the outersleeve 22 of a gripper 24, and a recessed pocket 26 to receive the innersleeve 28 of gripper 24 to permit a degree of axial movement of theinner sleeve 28 relative to the outer sleeve 22 which is fixed inposition. Protruding outwardly from opposing positions on either side ofthe body is a pair of bosses 30, for mounting a component to the body(not shown). The mountable component may comprise any suitable item orcomponent which includes mating members for attachment to the bosses. Itis contemplated that a useful application for the clamp is to fasten anoptical instrument for use by optometrists to measure a patient's eyes.However, this is but one example of a suitable application. As will beseen in FIG. 5, the bosses may be provided with a lock 32 to fasten thecomponent 33 to the bosses, and a pivot mount 34 to permit pivoting ofthe component. The component 33 is shown here as comprising an elementof an optical system for measuring patient eyes. It will be readily seenthat this is but one example of the many possible applications of theclamp.

The shaft 14 extending through the central bore 12 is of any suitablematerial in cross-sectional configuration. It is contemplated that theshaft 14 is cylindrical, but it will be seen that the system may beadapted for use with shafts having other cross-sectional shapes.

Inserted within each recess is a gripper 24, the preferred type being asomewhat modified version of the gripper sold under the trade-mark “GripFast™”. As seen in detail in FIG. 6, the gripper 24 comprises concentricinner and outer sleeves 28 and 22. The inner sleeve 28 includes aplurality of openings 29 to each receive a bearing 31 capable ofextending partway through the openings 29. The outer sleeve 22 isassociated with a wedge-shaped member 35 in contact with the bearings 31such that when the sleeves are aligned the member 31 urges the bearings31 partway through the openings 29, so as to tightly contact the shaft14 to prevent axial movement of the shaft. A spring 37 or other biasingmeans urges the sleeves towards their aligned, gripping position.

The shaft diameter must be selected so as to match the appropriate shaftsize for the gripper 24. In its normal rest position wherein the innerand outer sleeves 28, 22 are aligned, the bearings are urged inwardlyagainst the shaft 14 so as to lock the shaft, by means of an array ofwedges which contact the bearings. Displacement of the inner sleeves 28towards each other, namely inwardly towards the mid-line of the body,causes the bearings to retract thereby releasing the shaft 14 for freerotational and axial movement. Within the body 10, the outer sleeve 22contacts the shoulder 20 to prevent movement as the inner sleeve 28 isurged towards the mid-line of the body 10. The inner sleeve 28 ispermitted a degree of free travel, within the pocket 26. The pocket 26terminates at its base in a shoulder 40 for contacting the inner sleeve28 at a suitable point to prevent excess movement. The grippers 24 arespring biased so as to return their normal, locked position unless urgedinto their displaced, unlocked position by means to be described below.

The grippers selected in this embodiment permit the shaft 14 to rotatewhen locked. However it will be seen that a different choice of gripperwould prevent rotation of the shaft when locked.

The outer surface of each gripper 24 is covered by an annular disc 44which retains the gripper in position within the recess 16. The disc 44is retained by a snap ring 46, which fits within an annular groove 48within the recess 16.

The inner sleeves 28 of each gripper 24 may be displaced so as torelease the shaft by means of a push collar 50, consisting of a tubularmember 52 axially aligned with the grippers 24, the central bore 54 ofwhich receives the shaft 14. The collar 50 has an outside diameterslightly smaller than the inner sleeve 28 diameter, such that urging ofthe collar 50 against the inner sleeve 28 serves to displace the innersleeve 28 inwardly towards the mid-line of the body 10 so as to releasethe shaft 14. A flange 56 at the outer rim of the collar 50 has a flatoutside surface 58 to provide a relatively contact area for the actuatorarms 60, discussed below. The collars 50 each slide freely along theshaft, and are retained in position by contact with the actuator arms60. A pair of actuator arms 60 is provided to urge the collars 50inwardly towards the mid-line of the body 10 so as to release thegrippers 24. Each actuator arm 60 comprises a plate-like limb 62(a)arranged parallel to a respective end of the body 10 and spaced aparttherefrom, for contact with a corresponding collar 50. A first of thearms 60(a) is generally L-shaped, with a second limb 62(b) at rightangles to the first, for support a solenoid driver 64, discussed below.The second arm 60(b) is generally T-shaped, having an extended firstportion 70 for supporting a solenoid plunger 75 opposed to the solenoidmotor 66, and a second portion 72 for attachment to the body 10. Thearms 60 are both mounted to the body 10 for vertical sliding movementalong the axis of the shaft 14, for moving the collar 50 and innersleeve 28 of the gripper 24 within a vertical direction (all directionalreferences being relative to the shaft 14 being vertical). Mounting iseffected by mounting the first part of each arm 60 to one or more guidepins 71 which protrude outwardly from the body 10. Each guide pin 71fits within a corresponding recess 72 and is fixedly mounted within therecess. The actuator arms slide freely on the pins, through openings 74extending through the corresponding arms. A stopper 76 at the end ofeach pin 71 limits travel of the arms 60 along the pins 71. The guidepins 71 are preferably fabricated from stainless steel and are providedwith a mirror-like finish so as to provide smooth travel of the arms 60.

Vertical travel of the arms 60 is effected by a solenoid 64 mounted tothe second, vertical limb of the first arm 60(a). The solenoid in thiscase is a Guardian™ 102 oz. It will be readily seen that the particularselection of solenoid or other linear actuator will depend on thedesired application of the clamp and other obvious design constraints.

The solenoid motor 66 includes a plunger 75 extending verticallydownwardly. The plunger 75 is pivotally mounted to an elongate pivotblock 76, with the pivotal movement between the plunger 75 and pivotblock 76 compensating for any misalignment of the moving components. Thepivot block 76 in turn has a screw-threaded aperture 78 at its lowerend, to receive a mounting screw 80 extending upwardly from the secondactuator arm 60(b) so as to rigidly mount the pivot block 76 to thesecond arm 60(b). The adjusting screw 80 permits vertical heightadjustment of the pivot block 76 so as to permit adjustment of thevertical travel of the respective actuator arms 60. The typical verticaltravel of the arms 60 is about 0.076 inches for the first arm 60(a) andabout 0.088 inches for the opposing arm 60(b).

In operation, the solenoid 66 may be actuated to release the shaft 14.In the normal, rest position, the solenoid 66 is retracted therebymaintaining the shaft 14 in the gripped, non-moving position relative tothe clamp body 10. When actuated by a control system or directly by auser, the solenoid 66 retracts, thereby urging the opposed arms 60(a)and (b) towards each other and in consequence displacing the innercollar of each gripper towards an inboard direction relative to theouter collar. When sufficiently displaced, the shaft is released forfree rotation and axial movement.

It will be seen that a modification of the invention provides a devicewherein a release of the clamp permits only rotary or only axialmovement of the shaft 14 relative to the clamp body 10. For example, theshaft 14 may be provided with an anti-rotationary member such as a ribor a flat in operative communication with a corresponding receivingmember such as a slot or a corresponding flat within the grippers 24,thereby permitting axial movement but preventing rotation. In acorresponding fashion, the shaft 14 and clamp bore 12 may be providedwith mating annular flanges and grooves, permitting rotary movement ofthe shaft when released but preventing axial sliding motion.

It will be further see that the solenoid 66 may be controlled by anysuitable control system, including a simple user-operable switch, or acentral processing unit associated with other componentry. It will alsobe seen that any convenient linear actuator may be used in the positionof the solenoid 66.

It will be seen that although a detailed description of individualembodiments has been presented, the present invention is not limited toany feature, element or principle of operation described in particulardetail. Rather, the full scope of the invention is presented in thispatent specification as a whole, including the claims and furtherincluding any structural or functional elements equivalent to thosepresented herein.

1. A clamp for releasable locking engagement with a shaft, comprising aclamp body having a bore extending therethrough to slidingly receive ashaft to permit the clamp and body to slide along said shaft whenreleased, a pair of opposing shaft grippers coaxial with said bore forselectively gripping said shaft when actuated, each said grippercomprising inner and outer sleeves slideable axially relative to eachother, wherein axial displacement releases or engages said shaft, saidgrippers being in opposing relation to each other wherein gripping andreleasing of said shaft is effected by a coordinated displacement ofsaid inner sleeves towards or away from each other; a pair of opposingplungers slideably engaged to said body for displacing said innersleeves inwardly towards or away from the mid-line of said body, and apair of opposing arms in effective contact with said plungers andslideably engaged to said body, for effecting coordinated displacementof said plungers, each said arm associated with an actuator for acoordinated diverging or converging of said arms so as to grip orrelease said grippers to said shaft.
 2. A clamp as defined in claim 1,wherein said actuator comprises a solenoid having a solenoid bodyengaged to a first of said arms, and a solenoid plunger operativelyengaged to the second of said arms wherein extension of said plungerdiverges said arms and contraction of said plunger converges said arms.3. A clamp as defined in claim 2, further comprising a pivot blockpivotally mounted to said solenoid plunger between said first and secondarms for absorbing misalignment therebetween.
 4. A clamp as defined inclaim 1, wherein said grippers are arranged for release of said shaftwhen said inner sleeves are each displaced in an inboard direction.
 5. Aclamp as defined in claim 4, wherein said inner sleeves are biased toreturn to an outboard position when said plungers are retracted.
 6. Aclamp as defined in claim 1, wherein each of said grippers is retainedwithin said body within a recess open to a corresponding end of saidbody, each said recess coaxial with said bore.
 7. A clamp as defined inclaim 1, further comprising at least two guide pins protruding outwardlyin opposed directions for engaging said arms slideably to said body. 8.A clamp as defined in claim 1, wherein said grippers each comprise aplurality of openings in said inner sleeves, a plurality of shaftcontact members extending partway through said openings for selectivelycontacting and gripping said shaft when urged partway through saidopenings, and at least one wedge associated with said outer sleeve forurging said members through said openings when said outer and innersleeves are displaced relative to each other.
 9. A clamp as defined inclaim 1 wherein said grippers permit rotational but not axial movementof said shaft when engaged.
 10. A clamp as defined in claim 1 whereinsaid grippers permit axial but not rotational movement of said shaftwhen engaged.
 11. A clamp as defined in claim 1 wherein said gripperspermit neither axial nor rotational movement of said shaft when engaged.